Prior to the present invention, a conventional vane pump primarily used in machine tools and industrial machines includes, as shown in FIG. 1, in a cylinder body (2) a rotor having a number of vane grooves (10) formed on a peripheral surface thereof and driven by a rotor shaft (5). Vanes (12) are slidably received in the vane grooves (10) for radial reciprocating motion, and a hollow cylinder (6) is formed in the peripheral direction of the rotor (4) and abuts the front-end section of the vanes (12) fitted in the vane grooves (10) of the rotor (4).
A crescent-shaped pump chamber (8) is formed between the rotor (4) and the hollow cylinder (6) because the rotor (4) is eccentrically installed relative to the hollow cylinder (6). The volume of the crescent-shaped pump chamber (8) varies with the rotation of the rotor (4) due to the eccentricity.
When the rotor (4) is rotated by the rotor shaft (5), vanes (12) slidably received in the vane grooves (10) protrude from the center of the rotor (4) toward the hollow cylinder (6) due to centrifugal force so that the vanes (12) are in abutment with the inner surface of the hollow cylinder while the rotor (4) rotates.
Vane pumps operating in the above mentioned manner intake fluid to be compressed at an intake section (13) in which the volume of the crescent-shaped pump chamber (8) increases gradually and exhaust it at an exhaust section (14) in which the volume decreases gradually.
In the structure of such a vane pump, oil which flows from the exhaust chamber of a rear body (not shown) through an oil distribution channel of a vane back pressure chamber to the lower part of the vane grooves (10) in the rotor increases an abutting force between the front end section of vane (12) and the inner surface of the hollow cylinder so that a backward flow of fluid to be compressed is prevented.
But the structure of the prior art vane pump presents a problem in that, at high speed rotation, as the pressure of the fluid to be compressed increases, the adherent frictional force between the front end section of the vane (12) and the inner surface of the hollow cylinder (6) increases, which causes rapid and severe wear and burning between the vanes (12) and the inner surface of the hollow cylinder (6). The life-cycle of the vane pump is thus reduced.